The present invention relates to a foam generating nozzle and, more particularly, to a high flowrate foam generating aspirating nozzle which produces an improved quality of foam.
The foaming of liquid solutions has received wide attention over the years in several fields of application, including the agricultural and fire fighting fields, and in the cooling of hot materials. As to the latter application for example, foam generating nozzles have been employed to cool hot moving rolled steel because it has been discovered that foamed liquids exhibit increased cooling properties.
A wide variety of foam generating nozzles have been employed in the past with satisfactory results in a wide range of applications. Typical of such prior art nozzles which have generally enjoyed success in most applications are the nozzles and methods disclosed by Conrad et al. in U.S. Pat. No. 3,836,076. However, in certain foam applications, such as in the cooling of hot sheet steel, substantially increased cooling rates are needed, requiring increased liquid flowrates ---- flowrate levels which are substantially greater than those encountered in most typical foam nozzle applications. At these substantially increased flowrates, it is generally necessary to increase the wall thickness of the nozzle body. When the nozzle body wall thickness is increased, the result is an increase in the length of the air aspirating passages through which the air is drawn into the nozzle body for intimate mixing with the liquid foam producing agent to produce the desired foam. This increase in air inlet aspirating passage length has been found to result in a substantial deterioration in the quality of the foam from the quality that is enjoyed in the lower flowrate foam generating nozzles.
In the present invention it has been discovered that, if the air aspirating passages which were typically of constant width in the past are tapered toward the exterior of the nozzle body so as to present a wider width adjacent the exterior, the quality of the foam which is generated by the nozzle is substantially improved.
In one principal aspect of the present invention, a foam generating nozzle comprises a nozzle body having an elongate passage therein and a liquid inlet adjacent one end of the elongate passage for introducing a liquid foam producing agent to flow axially through the elongate passage. At least one gas inlet passage extends through the nozzle body between the liquid inlet and the other end of the elongate passage for aspirating a gas into the passage when the liquid foam producing agent is flowing through the elongate passage. The gas inlet passage extends in a plane substantially perpendicular to the axis of the elongate passage and has a first width adjacent the elongate passage, a second width greater than the first width adjacent the exterior of the body, and a wall extending between those widths. The nozzle also includes foam discharge means adjacent the other end of the body for discharging the foam therefrom.
In another principal aspect of the present invention, the aforementioned liquid inlet comprises a pair of orifices for discharging liquid foam producing agent into the elongate passage so as to flow axially through the elongate passage and past the gas inlet passage, the pair of orifices being spaced radially from each other and from the axis of the elongate passage, and a pair of the gas inlet passages extending radially relative to the axis of the elongate passage and positioned transversely from the pair of orifices.
In still another principal aspect of the present invention, the aforementioned gas inlet passages comprise two portions, one portion extending radially outward from the elongate passage and having a width which is substantially constant over its length and that width is the aforementioned first width, and a second portion having the second width.
In still another principal aspect of the present invention, the aforementioned second portion comprises a wall which tapers between the first portion and the second width adjacent the exterior of the body.
In still another principal aspect of the present invention, a method of generating foam comprises discharging a liquid foam producing agent into an elongate passage to flow axially therein, flowing the liquid foam producing agent past a gas inlet passage which extends in a plane which is substantially perpendicular to the axis of the elongate passage and which has a wall which tapers between a first width adjacent the flowing liquid and a second width which is greater than the first width and which is spaced from the flowing liquid, and aspirating a gas into the flowing liquid foam producing agent through the tapered gas inlet passage to discharge the gas into the flowing liquid at the first width of the gas inlet passage.
In still another principal aspect of the present invention, in the foregoing nozzle and method the ratio of the first width of the gas inlet passage to the cross-sectional width of the elongate passage is approximately 0.17-0.23.
In still another principal aspect of the present invention, in the foregoing nozzle and method the ratio of the first width to the second width is approximately 0.3-0.5.
These and other objects, features and advantages of the present invention will become evident upon consideration of the following detailed description.